Stevie, it has to shift seasonally, at least. Water, snow and icefall gets behind it from the top and both sides; there are also chockstsones to help in a ratcheting-out effect. Once again repeating, here is a picture showing some crushed tubes and a hex found at the base of the Hourglass the spring after they had been fixed in place for some unusual reason and left behind. This might be Vern C.